Preselector tuning system



M. FLAHERTY4 PRESELECTOR T UNING SYSTEM 2 sheets-shea 1 Fil'edduly 2. 1952 Feb. 20, 1934. M. FLAHERTY I PRSELECTOR TUNING SYSTEM Filed July 2. 195g 2 sheets-sheet' 2 Page.'

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Patented Feb. 20, 1934 UNITED STATES,`

PATENT oEFlcE 1,943,313 raEsELEc'roa TUNING SYSTEM Mark Flaherty, Haddon Heights, N. J., assigner to General Electric Company, a corporation of New York Application July 2, 1932.- Selial N0. 620,652

17 Claims'. (Cl. 'M -14) My invention relates to 'mechanical prese- It has been proposed heretofore to tune a cam was turned to such a position by the lever that the roller becameseated in the notch of the heart-shaped cam.

It has been found, however, that diiculties are encountered when the movement of the roller into place'between and in contact with the operating portions of the notch of theheartshaped cam is depended on as a cam positioning means. Even Very slight inaccuracies in the roller and in the cam surfaces in the region of .the notch have been found -sufllcient to cause a wide variation in the -iinal or operating posi-- tion of the cam and therefore a correspondingly wide variation in the adjustment of the tuning y element connected to the cam.

In accordance with my invention this diiliculty is overcome by the provision of cooperating positioning members which are mounted respectively on the cam and on the operating lever, and which serve to center the cam shaft finally and accurately after the cam has been rotated nearly to its centered or operating position by the roller of the operating lever. Seating of the contact member or roller in the cam notch is vthus no longer depended upon for Vthe iinal accurate centering of the cam and for the final setting of the tuning element to which the cam is connected.

In the preselector tuning arrangements heretofore proposed employing the heart-shaped cam difiiculties have also been encountered due to the fact that the contour of the cam was such that the cam Was not easily moved by the operating lever in the Vprocess of selective tuning to a predetermined frequency. Because of this unsuitable cam contour the lever pressure required to drive the cam throughout its range of travel was not approximately uniform. On the contrary, the pressure rose to a relatively high value in certain portions of the cam rotation thereby causing jerky and uncertain action and hard starting of the cam in certain positions.

In accordance with my invention the above `diiculty of uncertain and uneven action in the preselector tuning arrangement due to the contour of the heart-shaped'cam is overcome by the provision, in the preselector tuning arrangement, of a cam of such contour that regardless of its initial position the cam is readily started by moderate pressure of the lever, and that the cam is moved easily throughout its entire range of travel. To this end the cam is so formed that the lever pressure required to start the cam is not only relatively low atall positions thereof but appears substantially uniform throughout the cam travel, varying through only a relatively small range for different cam positions.

In carrying out the design of the heartshaped cam in accordance with my invention the cam surface is so formed and the lever and roller are of such dimensions and so placed with respect to the cam that the line passing through the roller center and normal to the cam periphery forms, as the cam is rotated through line drawn through the center of the cam and 9 the center of the roller. l

For example, the ca'm is preferably-so formed and the lever and its roller so arranged with respect to the cam that when the lever is actuated to cause the roller to rotate the cam in a given direction through a portion of its range 4from its extreme open positionv to its closed or centered position, the angle between the line normal to the cam through the roller center and the radial line through the cam center and roller center may be substantially constant or this angle may increase progressively by a relatively small amount as the cam is rotated from its extreme open position to a position in which the' line through cam center androller center 55 selector device ready for the operation of tuning is in the direction of the line at a right angle to the lever axis. Then as this point of the cam travel is reached and the cam is rotated through the remainder of its travel to its cen- .tered position, the angle between the line normal to the cam through theroller center 'and the line at a right angle to the lever axis may be v "tions, a plurality of heart-shaped cams 15, each substantially constant or may decrease progressively by a small amount as the cam approaches its centered position.

As the cam turns through the approximately half-revolution from the open to the centered position, the above-mentioned .line passing through the roller center and normal to the cam periphery is directed in turn to different cam periphery center points within the cam area. these center points being at progressively smaller predetermined distances from the cam center and located on radial lines drawn from fthe. cam center and spaced a predetermined number of degrees about this center.

A further feature, in accordance with my invention, of the preselector tuning arrangement employing heart-shaped cams actuated by levers is the provision of arc-shaped levers forv this purpose having finger notches, whereby the preselector device is adapted for use in connection with a radio receiver having a panel opening, the arc-shaped levers ,being so arranged as to form closure members for the panel opening.

In the use of the tuning arrangement in which a plurality of heart-shaped cams are mounted on the shaft of a tuning element, each cam must rst be rotated loosely on the shaft to a predetermined tuning position corresponding to a given frequency and then firmly locked in this position. It is therefore a still further feature of my invention to provide an improved means for locking the heart-shaped cams, together with their attached centering means hereinbefore mentioned, to the shaft of the tuning element.

My invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring t'o the drawings, Fig. 1 is a perspective view of a portion of aradio receiving apparatus in which my invention has been embodied; Fig. 2 is an end view partially in section of the preselector tuning device shown in Fig. 1, showing a heart-shaped cam in position for locking on the shaft of a tuning element; Fig. 3 is similar to Fig. 2 but showsrthe prethe radio apparatus to a desired frequency; Fig. 4 is an exploded view of a heart-shaped cam and associated parts shown in Figs. 1 Vto 3; Fig. 5 is a diagrammatic view illustrating the design of a heart-shaped cam in accordance with my invention; Fig. 6 is 'a diagrammatic view of a modified cam design in accordance with my invention; and Fig. 7 shows-curves illustrating the relation of impressed lever pressure to degrees of rotation of the cams illustratedin Figs. 5'and 6.

In Fig. 1 the numeral 10 designates a radio receiving apparatus comprising a tuning condenser element 11 the rotor of which (not shown) is mounted on a shaft 12 which is adapted to be rotated by the-operator through any suitable means, as by a control knob 13, to tune the receiver in the usual manner to any desired frequency or station indicated onv a dial 14.

In order to provide preselector tuning whereby the tuning element 11 may be moved by one stroke of a lever from any position which this tuning element may occupy to any one of a plurality of predetermined positions corresponding to the different frequencies of a plurality of transmitting or broadcasting stacorresponding to a different one of the predetermined frequencies to which the receiving apparatus is to be tuned, are mounted on the tuning element shaft 12. To move the cams into operating position a plurality of levers 16 are mounted on a shaft or pivot 17 and are provided with rollers 18, better shown in Figs. 2 and 3, arranged to bearA upon the peripheries of thecams when the levers are moved about the pivot 17. 'I'he tuning element 11 will be tuned to a given frequency when the cam corresponding to this frequency is in the position shown in Fig. 2, the roller-'being in the region of the cam notch 19 when the cam is in this illustrated position.

In previous preselector tuning systems comprising heart-shaped cams acted on by a series of levers the centering and locking of each cam in its operating position' similar to the position illustrated in Fig. 2 was accomplished, as hereinbefore explained, merely by the entering of the operating lever roller into the cam notch and by the contact of the roller with the cam surfaces within the notch. With this latter arrangement even very slight inaccuracies in the roller and in the contacting surfaces in this region of the cam, in which region the cam radii are short, caused a wide variation from accurate positioning of the element which was intended to be moved to tuning position by the cam and lever arrangement.

`In my cam and lever arrangement described and claimed herein the cam'is not finally centered by the entering of the roller 18 into the cam notch 19 but bythe coaction of the lever 16 with a centering and locating member 20 fastened to the cam, as by rivets 21. Locating member 20 comprises an anvil portion 22 presenting a contact surface or surfaces preferably adjacent the notch of the cam. In the embodiment of my invention herein shown and described, the locating member or anvil 22 comprises a pair of contact portions or anvil blocks 23 on either side of the cam notch 19. A portion of the lever 16 is arranged to strike the blocks 23- to center the cam, in a manner be more fully explained hereinafter. A

In preparing preselector tuning apparatus comprising heart-shaped cams for use in tuning the receiving apparatus to predetermined frequencies means must be provided to lock each cam securely to the shaft of the tuning element at a detlnite point in the rotation of the shaft. For this purpose I have provided an improved locking means which is combined with the cam centeri `and locking means above described compr inglocating member 20. This locking means comprises a locking lug 24 hav ing a hole 25 formed therein throughv which passes the shaft 12 of the tuning element 11, and having a threaded shank or stud portion 26 passing through a wall portion 27 of the locating member 20, the locking lug 24 being tightened by a locking nut 28 on the stud 26. The member 20 is preferably U-shaped, the legs of the U preferably having clamping surfaces 29 forming wedge-shaped recesses or openings.

vtuning element shaft 12 preparatory to utilizing the preselector arrangement for tuning the receiver toa predetermined frequency by one.

stroke of a lever 16, the receiver is first tuned to a desired frequency in the usual manner by the manipulation of the control knob 13 which rotates the shaft 12 connected to tuning element 11 to a position corresponding to this desired frequency. The operating lever 16 corresponding to a given cam is then depressed to bring roller 18 in contact with the cam which at this time is loose on shaft 12, the pressure exerted through the roller causing the cam to rotate on the shaft from any position it may have occupied to near its centered or operating position. As the cam nears this operating position on shaft 12 a portion 31 of lever 16 which coacts with the locating member 20 in the centering operation approaches and finally comes in contact with member 20. This coacting portion 31 of lever 16 is preferably a straight-edge or flat member integral with the m'ain body of the lever. The straight-edge or flat lever membei 31 in approaching the locating member 20 rst strikes one or the other of the anvil blocks 23, depending on the previous position of the cam. As the lever continues its movement toward member 20 the cam, which is fastened to the member 20, is moved through a short arc into its final centered position on shaft 12. In this final centered position of the cam the lever member or portion 31 is firmly pressed against the opposite extremities of the front side of the locating member 20,' or against the oppositely disposed anvil blocks 23 when the member 20 is cut away on its front side as shown to form such contact or anvil blocks.

With the cam thus ilrmly held in its proper position on shaft 12 a wrench" or key 32 is applied to the nut 28 and the locking lug 24 is tightened. thereby clamping the shaft 12 between the wedge-shaped surfaces 29 and 30 of the U-shaped member 20 and the lug 24 respectively. After the cam, fastened to locating member 20, is thus locked in its proper position on shaft 12 for the frequency to which the receiver was tuned, the operating lever A16 is released and is then returned toits normal nonoperating position by a spring 33. The above- .described operation of setting a cam 15 may then be repeated for as many other frequencies as are provided for by additional cams and levers similar to cam 15 and lever 16.

In order to tune. the receiver 10, by a single stroke of a lever. to a given frequency for which the preselector tuning arrangement has been previously set as above described, the operating lever as 16, Fig. 3, corresponding to this given- `positively and accurately to its exact centered position shown in Fig. 2. In order to insure that the nal few degrees of cam rotation and the locking of the cam into exact centered position shall be accomplished by the coaction of the cam locating member 20 and lever member 31 alone without interference from possible contact of roller 18 with the cam surfaces in the region of the cam notch, the cam` surface is relieved or cut away slightly at the notch, or otherwise formed to avoid contact between the roller and the cam in this region.

The operating lever 16 through which pressure is exerted on the heart-shaped cam 15 preferably comprises, in, addition to a main lever portion 34 pivoted at 17 and provided with roll- Ver 18, a panel closure portion 35 connected as by rivets 36 to the extremity of main lever portion 34 remote from the pivot 17. 4This closure portion 35 extends through and fits closely within a relatively wide and long opening 37 formed in the panel 38 of the receiving apparatus 10. The closure portion 35 may be in the form of a channel member having a relatively wide cylindrical face and bent in an arc of a circle having pivot 17 as a center. To permit the operator to move the lever 16 from outside the apparatus 10, the arc-shaped closure portion 35 of the lever 16 must be provided with actuating means with which the hand or finger of the operator makes contact. For this purpose in the present embodiment of the invention the actuating means is integral with the closure member 35, this member being indented to form finger notches 39 therein. h

In operation of the lever system comprising arc-shaped closure member 35, when the lever 37 is drawn back by spring 33 to its neutral or non-operating position shown in Fig. 3, as determined for example by an adjustable stop screw 40, the finger notch\39 is near the top 0f the panel opening 37. When arc-shaped member 35 is pulled down, by means of the finger notch 39, to rotate the lever 37 on pivot 17 to the position in which the cam l5 is centered, as hereinbefore described and as shown in Fig. 2, the. closure member 35 comes to rest with the notch 39 adjacent the lower end of panel opening 37. The closure member 35 may be perforated as at 41 to provide easy access of the wrench 32 to the locking screw 28 in the operation of preliminary locking of the cam 15 to the shaft 12.

In the explanation of the design of a cam in accordance with my invention, as illustrated in Fig. 5, the cam itself is assumed to be held stationary and the lever and roller are assumed to be moved around the cam. From the cam center 42 are drawn radial lines spaced for example 10 apart. A radius oraxis line 43 for the lever is taken, the lever-having a pivot point at the center of pivot 17 at one end of the radius 43 and a roller center on rollervl at the other end of the radius. The roller is now assumed to be moved between positions 19 and 1' through positions wherein the center of the roller 18 intersects the successive radial lines 44 spaced 10 apart. These positions, therefore, correspond to positions of equal angular movement of the cam when the cani is the member which is rotated. The corresponding positions of the centerv ofthe pivot 17 in its assumed motion about the cam are indicated onv the drawings by corresponding numerals 19" to 1' on the circumference 45 Qn which the pivot 17 is assumed to move.

The cam surface in the arrangement so far described in connection with Fig. 5 is so formed and the lever is so arranged with respect to the cam that when the lever` and roller are assumed to be moved from approximately position 19' to approximately position 8 the line of direction of the force normal to the cam, and indicated in Fig. 5 by the arrows, is at a nearly constant angle with the radius lines 44 passing through the cam center 42 and the center of the roller. In the embodiment of the inventionl shown in Fig. 5 this angle increases by a relatively small amount 'from positions of the roller near the apex of the cam, for example position 18 or 19' to approximately position 8. At approximately position 8' the radius line passing through the cam center 42 and center of roller 18 is in the same direction as the line at a right angle, at the center of the roller, to the radius or axis 43 of the lever. When the lever and roller are then assumed to be moved from approximately position 8', the line of direction of the force normal to the cam and indicated by arrows is at the same above-mentioned nearly constant angle with the lines 46 which are at a right angle, at the center of roller 18, to the radius or axis 43 of the lever. This latter angle between the line of force normal to the cam and the line at a right angle to the lever axis 43 decreases by a relatively small amount as the roller is assumed to move from approximately position 8' to that position at which the roller is close to the closed or centered position of the cam, for example position 2'.

By so arranging the lever that its pivot 17 is slightly closer to the cam center 42 than hereinbefore described in connection with Fig. 5 the angle between the line of the force normal -to the cam and the line at a right angle, at the center of the roller, to the axis 43 of the lever is increased in the region of the roller positions near the cam notch. Thus, in Fig. 5, a new circumference 47, which the pivot 17 describes about cam center 42 as the lever is assumed to move about this center, may be drawn which is closer to the center 42 than is the circumference 45. Positions 2" to 19" of pivot 17 on circumference 47 correspond to positions 2' to 19' on circumference 45. The new circumference 47 may be closer to center 42 than is circumference 45 by such an amount that at the new position 2" of pivot 17 the angle between the line of the force normal to the cam and the line 48, at a right angle, at the center of the roller, to the axis 43 of the lever is increased, over the corresponding angle between these lines when the pivot 17 is in position 2', sufficiently to make the above angle at roller position 2' substantially the same as the corresponding angle at or near roller position 7'. At the same time it will be seen that the radius line passing through the cam center 42 and the roller center will be in the same direction as the line at a right angle to the lever axis 43 at a ro'ller position somewhat nearer the cam notch, i. e., at approximately position 7' of the roller 18 instead of at approximately position`8 which is the case when the pivot 17 is assumed to move in the circumference 45. Further, it will be seen that for roller positions 19 to 8' corresponding to the new pivot positions 19" to 8" on circumference 47 the angle between the line of the force normal to the cam, and indicated by the arrows, and the radius line passing through the cam center 42 and the roller center is the same as in the preceding case in which the pivot 17 is assumed to describe the circumference 45.

Thus, in that cam and lever arrangement iIIustrated in Fig. 5 in which the pivot 17 is mounted closer to the cam center 42' than in the arrangement Ilrst described herein, the angle between the line of the force normal to the cam and the cam radius passing through the roller center increases by a small amount as the roller is assumed to be moved from its position 19' to position 7. Thereafter the angle between thc line of the force normal to thecam and the line at a right angle, at the roller center, to the lever axis remains substantially constant as the roller is assumed to move from its position 7' to its position 2'.

From the above description of the two cam and lever arrangements shown in Fig. 5 it will be evident that in both cases the angle between the line of the force normal to the cam is nearly constant, as the cam moves from its open position, for example at approximately position 18' of the roller, to a position intermediate the open position and the closed or centered position, and that this nearly constant angle is substantially the saine as the nearly constant angle between the line of the force normal to the cam and the line at a right angle to the lever axis at the roller center, as the cam moves from the abovementioned intermediate position to its closed or centered position.

The lines of direction of the forces normal to the cam as indicated by the arrows in Fig. 5 are such that different groups of these lines converge toward different cam surface center positions 49 to 53 which are within the cam area. In the present example these points are located on radial lines drawn from the center 42 of the cam and spaced 45 apart, points 49 and 53 being located on the minor axis 54 of the cam and on opposite sides of the center 42.

Referring to the lines normal to the cam Vand indicated by the arrows at positions 1 to 19', for positions 2', 3' and 4' these lines are directed toward the point on the cam indicated at 49 as the roller is assumed to move through the angle a. For the next group of positions, 5', 6', 7', 8 of the roller the lines normal to the cam are directed toward the new center 50, farther out from the center 42 of the cam, as the roller moves through the angle b. The similarly succeeding groups of lines normal to the cam, 9' to 13', 14' to 16' and 17 to 19' are directed respectively to the center points 51, 52, 53 located at progressively greater distances from the cam .center 42, the roller being assumed to move through the angles c, d, e in turn.

In the actual construction of a heart-shaped cam the design of which is illustrated in the diagrammatic view of Fig. 5, the cam periphery center points 49, 50, 51, 52, 53 are located respectively approximately 116-", 1/2" and 5/8" from the center of the cam and on radial lines spaced 45 apart as hereinbefore described, and the radial distances fromO center points 49 to 53 to the corresponding portion of the cam periphery, comprised between angles a to e respectively, are approximately 5%", b", l", 1% and 1H". The length of the radius or axis 43 of the lever is approximately 21/8", the diameter of the roller 18 is approximately and the distance from cam center 42 to the center of pivot 17 is approximately Zg" when the pivot is assumed to describe the circumference 45 about the cam center.

In Fig. 6 -is shown a heart-shaped cam formed in accordance with my invention and similar to 1,948,378 f I it will be readily apparent by inspection o theithe cam shown in Fig. 5 but differing therefrom in that the cam periphery center points are all located on the camv radii drawn in that portion of the cam area between the minor axis and the apex of the cam. These center points, 56

to 59, are located `respectively approximately 1/4", 9/32", 23/64 and '1/,165 from the cam center 60. The radial distances from the center points 56--59 to the corresponding portion or the cam periphery are respectively approximately 1/2", 3/4", 61/64", and 1 5/16", and the radial lines on which the center points 56 to 59 are located are spaced respectively approximately 20, 80, 110 and 160 about the cam center 60 from the minor axis 55.

The distance between the pivot center and the roller center'of the lever with which the cam shown in Fig. 6 is associated may be 21/8", the diameter oi the roller approximately and the distance from the cam center 60 to the lever pivot approximately 21%", all substantially as in the n arrangement shown in Fig. 5. When the cam of Fig. 6-is rotated by the lever arranged as described the angle between the line of the force normal to the cam and the radial line .through the cam center 60 and the center of the roller is substantially constant or increases by a small amount as the cam rotates from its open position to a position intermediate its open position andits closed or centered position. At this intermediate position the radial line through the cam center 60 and the roller center coincides with the line at a right angle, at the roller center, to the lever axis. As the cam rotates from this intermediate position to its closed or centered position the angle between the line of the force normal to the cam and the line at a right angle, at

the roller center, to the lever axis is substantially constant or decreases by a small amount.

The action of the `cam shown in Fig. 6 is, therefore, essentially similar to that of the cam shown in Fig. 5. The cam of Fig. 6, when the dimensions of the cams shown in Figs. 5 and 6 are as above stated, is, however, somewhat smaller than the cam of Fig. 5 and therefore does notv require as wide a movement of the lever to rotate the cam from its `open position to its closed or centered position.

In Fig. 'I the lower curve 61 shows the lever pressure found by actual test to be required to ment illustrated in Fig. 5, through the range 'of cam travel from open-to closed or centered position. It will be observed that the required lever pressure varies only slightly throughout the range. The upper curve 62 shows similarly the lever pressure required by test to rotate a cani of the form illustrated in Fig. 6 through` its range of travel. The latter curve 62 shows more variations oi pressure and a higher pressure throughout the range than the lower curve.

Nevertheless, it will be observed that even in the case of the cam of Fig. 6 corresponding to curve 62 the lowest pressure through the cam travel is 65% of the highest, whereas in the case of the cam of Fig. 5, corresponding to curve 61 the lowest pressure is 80% of the highest. In both cases the pressure variation is maintained within such relatively close limits that to the operator the finger pressure required on the lever appears substantially the same throughout the range of rotation of the cam. Further, in both cases, that oi" the cam shown in Fig. 5 and of the cam shown in Fig;`6,

curves 61 .and 62 that at no part or the'c'am travel is abnormally high pressureV required ft` Y start the cams, and that in the case of neither cam is to be found any 'tendency to blockingv v'off the cam movement by the pressure appliedv4 to tuning systems of radio receivers and like apparatus. It will be evident, however, that this mechanism may be employed to rotate the shafts of a wide variety of apparatus accurately and positively to any one of anumber of preselected positions.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a preselector device for radio receiving apparatus and the like, a heart-shaped ca m, a lever having a roller in contact with the periphery of said cam, said lever being adapted to exert pressure on said cam to -rotate the same through a predetermined range, manually operated means comprising an arc-shaped member connected to said lever having a ilnger notch formed therein, and means to 'center said cam in its closed or operating position comprising a-` positioning element connected to said cam and adapted to beiioved by said lever as the cam approaches said closedor operative position, said cam being so formed and said lever and roller being so arranged with respect thereto that the cam is moved throughout its range of travel with substantially uniform pressure on said lever.

2. In a preselector device comprising a heartshaped cam,- actuating means therefor including a contact member adapted to engage the periphery of said cam to rotate the same to approximately a predetermined Vcenteredposiing memben move a cam, in the cam and lever arrange- 3. In a preselector device comprising a heartshaped cam, a lever having a contact member adapted to rotate the cam, and a positioning member connected to said cam adapted to have pressure exerted thereon by said lever torotate the cam through a predetermined number of degrees substantially independent of said lever 5. In a preselector device comprising a heartshaped cam and a lever, a roller connected to, said lever adaptedrto be moved into contact with the periphery of .said cam to rotate the cam to an intermediate position close to a predetermined centered position in which the roller ioo enters the notch region of the cam, and a cam positioning and centering element connected to said cam including an anvil member having contact surfaces on opposite sides of the center of the cam, said surfaces being adapted to bepressed by a coacting surface of sat'd lever when said roller reaches a point on the cam periphery corresponding to the intermediate cam position to rotate said cam independently of said roller from said intermediate position to .said predetermined centered position.

-in the region of the notch of the cam, and cam positioning and centering means operative independently of said roller to rotate said cam from said intermediate position to a predetermined centered position, said means including a positioning element connected to said cam and having two anvil blocks one on either side of the center of the cam and a positioning element associated with said lever adapted to strike said anvil blocks.

7. In a preselector device comprising a shaft, a heart-shaped cam and a lever having a contact member adapted to rotate` the cam, a combined cam positioning and locking element adapted to have pressure exerted thereon by said lever to rotate the cam independently of said lever contact member, said cam positioning and locking element including a clamping member connected to the cam, a clamping member mounted on said first-named clamping member and movable with respect thereto, and means to lock said cam in a predetermined position on said shaft between said clamping members.

"8. In a preselector device comprising a shaft,

' a heart-shaped cam and a lever having a contact member adapted to rotate the cam, a combined cam positioning and locking element.

adapted to have pressure exerted thereon by said lever to rotate the cam independently of said lever contact member to a predetermined position of the cam, said cam positioning and locking element including a member connected to the cam and having clamping surfaces, a

'movable lug having clamping surfaces, and

' means to lock said shaft in a predetermined positionl on said shaft between the clamping surfaces of said member connected to the cam and the clamping surfaces of said lug.

9. In a preselector device lmounted within a casing having a panel, said vdevice comprising a heart-shaped cam and a lever'pivoted within said casing and adapted to actuate said cam from outside said casing, said lever projecting through an opening in said panel, actuating means for said lever including a member connected to said lever and projecting through said opening, said member forming closure means for said panel opening as said lever is moved to operate said cam.

10. In a preselector device mounted within a casing having a panel, a shaft, a plurality of heart-shaped cams, a pivot, a plurality of levers adapted to rotate about said pivot, each of said levers being adapted to actuate a different one of said'cams from outsidesaid casing, means to lock said cams on said shaft, each of said levers including a member@ having a relatively wide substantially cylindrical face pro- Jecting through a relatively wide and long opening in said panel and forming a closure member for said opening as said lever is rotated about said pivot through the range of travel of said cam, each of said cylindrical faces having a perforation formed therein providing access to said locking means from outside said casing.

11. In a preselector device mounted within a casing having a panel, a shaft, a plurality of heart-shaped cams, a pivot, a plurality of levers adapted to rotate about said pivot, each of said levers being adapted to actuate a different one of said cams from outside said casing, means to lock said cams on said shaft, each of said levers including a member having a relatively wide substantially cylindrical face projecting through a relatively wide and long opening of saidpanel, said member being in the form of an arc having said pivot as its center and providing a closure member for said opening throughout the range of travel of said cam, each of said cylindrical faces having a perforation formed therein providing access to said locking means from outside said casing.

12. In a preselector device mounted-within a casing having a panel, a shaft, a plurality of c heart-shaped cams, a pivot, a plurality of levers adapted to rotate about said pivot, each of said levers being adapted to actuate a diierent one of said cams from outside said casing, means to lock said cams on said shaft, each of said levers including a substantially arc-shaped member having a relatively wide substantially cylindrical face projecting through a relatively Wide and long opening of said panel and forming a closure means therefor as said cam is rotated throughout the range of travel thereof, each of said cylindrical faces having a perforation formed therein providing access to said locking means from outside said casing, each of said arc-shaped members having a finger-notch formed therein.

13. In a shaft positioning device for a preselector apparatus or the like, a shaft, a heartshaped cam mounted on said shaft, a lever having a contact member adapted to be moved into 12v. contact with the periphery of said cam to rotate the cam through a predetermined range,

said cam being so formed and said lever being so mounted with respect to the cam that as the cam is rotated by the lever from a prede- 12g termined open position to a position intermediate said open position and the closed or centered position of the cam the angle between the line of the force. exerted at said contact member normal tothe cam periphery and the radial line passing through the cam center and said contact member is substantially constant, and as the cam is rotated by the lever'from the intermediate position to the closed or centered position the angle between said line of the force exerted normal to the cam periphery and the line at a right angle to said lever at said contact member isv substantially constant and equal to said first-named angle.

14. In a shaft-positioning device for a pre- 14C selector apparatus, or the like, a shaft, a heartshaped lcam mounted on said shaft, a lever having a contact member adapted to be moved into contact with the periphery of said cam to rotate the cam from acpredetermined open position at which said contact member is adjacent the apex of the cam to the closed or centered position of the cam at which said contact member is in the region of the notch of the cam, said cam being so formed and said lever being so mounted with respect to the cam that as the cam is rotated by the lever from the open position to a position intermediate the open position and the closed or centered position the angle between the line of the force exerted at said Contact member normal to the cam periphery and the radial line passing through the cam center and said contactmember increases by a relatively small amount, and as the cam is rotated by the lever from the intermediate position to the closed or centered position the angle between said'line of the force normal to the cam periphery and the line at a right `angle to said lever at said contact member decreases by` a small amount, the'angle between said line of the force normal to the periphery and said radial line being equal at said intermediate position of the cam to the angle between said line of the force normal to the cam periphery and said line at a right angle to the lever at the contact member.

l5. In a shaft positioning device for a preselector apparatus or the like, a shaft, a heartshaped cam mounted on said shaft, a lever having a `roller adapted to be moved into Contact with the periphery of said cam to rotate the cam through a predetermined range, said cam being so formed and said lever and roller being so mounted with respect to the cam that as the cam is rotated by the lever from a predetermined open position to a position intermediate said open position and the closed or centered position of the cam the angle between the line of ,the force exerted at said roller normal to the cani periphery and the radial line passing ,through the cam center and the roller center is substantially constant, and as the cam is rotated by the lever from the intermediate position to the closed or centered position the angle between said line of the force normal to the cam periphery and the line at a right angle to said lever at the center of said roller is substantially constant and equal to said first-named angle.

16. In a shaft positioning device for a preselector apparatus or the like, a shaft, a heartshaped cam mounted on said shaft, a lever having a roller adapted to be moved into contact with the periphery of said cam to rotate the cam from a predetermined open position at which said roller is adjacent the apex of the cam to the closed or centered position of the cam at which said roller is in the region of the notch of the cam, said cam being soformed and said lever and roller being so mounted with respect to the Cam that as the cam is rotated by the lever from the open position to a position intermediate the 4open position and the closed or centered position the angle between the line of the force exerted at said roller normal to the cam periphery and the radial line passing through the cam center and the center of the roller increases by a relatively small amount, and as the cam is rotated by the lever from the intermediate position to thc closed or centered position the angle between said line oi the force normal to the cam periphery and the line at a right angle to said lever at the center of said roller decreases by a small amount, the angle between said line of the force normal to the cam periphery and said radial line being equal at said intermediate position of the cam to the angle between said line of the force normal to the cam periphery and said line at a right angle to said lever at the center of the roller.

17. In a shaft positioning device for a preselector apparatus cr the like, a shaft, a heartshaped cam mounted on said shaft, a' lever having a roller adapted to be moved into Contact with the periphery of said cam to rotate the cam from a predetermined open position at which said roller is adjacent the apex of the cam to the closed or centered position of the cam at which said roller is in the region of the notch of the cam, said cam being so formed and said lever and roller being so mounted with respect to the cam that as the cam is rotated by the lever from the open position to a position intermediate the open position and the closed or centered position the angle between the line of the force exerted at said roller normal to the cam periphery and the radial line passing through the cam center and the center of the roller increases by a relatively small amount, said angle at said intermediate position of the cam being equal to the angle between said line of the force normal tothe cam periphery and the line at a right angle to said lever at the center of the roller, and that as the cam is rotated by the lever from the intermediate position to the closed or centered position said last-named angle remains constant.

MARK FLAHERTY. 

